We have found the solution for this, hereby I’m commenting here so it might be helpful to someone in the future!
As I said, we had migrated our platform from hawthorn to Ironwood, after that we got this issue.
When we search for individual learners’ submission, the submission will be found on the bases of the user’s anonymous user-id. And anonymous user-id generating on the bases of the Secret key, which is present in lms.auth.json
So in our case secret key is different for both versions hawthorn and ironwood, that’s why we are not able to get the submissions of students.
Make sure to copy these settings from your previous versions!